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Polar Covalent Bond

What is a Polar Covalent Bond?

A covalent bond is formed when two atoms share electrons between them. The covalent bond is likely to be polar when the electrons are unequally shared. The skewness arises due to the difference in the electronegativities of the two atoms. Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. It is measured using a scale known as the Pauling scale and ranges from 0.7 to 4. The following table explains the type of chemical bond formed due to this electronegativity difference [1-10].

Type of Chemical BondElectronegativity Difference
Nonpolar covalent 0
Slightly polar covalent 0.1 to 0.4
Polar covalent 0.5 to 2
Ionic > 2

The more significant the difference in electronegativity, the greater is the polarity and the bond strength. Hence, polar covalent bonds have an intermediate bond strength.

Polar Covalent Bond

Properties of Polar Covalent Bonds

Here are some facts about polar covalent bonds.

  • Takes place between two nonmetals or between a nonmetal and a metalloid
  • Unequal sharing of electrons in a compound
  • Electronegativity difference between atoms is between 0.1 and 2
  • One end of the bond is positively charged, and the other end is negatively charged
  • Polar compounds dissolve in a polar solvent

Examples of Polar Covalent Bonds

Here are some examples of a polar covalent bond with the electronegativity difference between the two bonding atoms [1-6]:

Compound NameMolecular formulaBondElectronegativity difference [11]

Water

H2O

O-H

1.4

Hydrogen fluoride HF H-F 1.9
Hydrogen chloride HCl

H-Cl

0.9

Hydrogen bromide

HBr

H-Br

0.7

Ammonia

NH3

N-H

0.9

Sulfur dioxide

SO2 S=O 1
Hydrogen sulfide H2S H-S 0.4
Methanol CH3OH O-H 1.4

An explanation of the polar covalent bond in some compounds is given below.

1. Water (H2O)

Water is a polar solvent. A polar covalent bond is created when the oxygen (O) atom, being more electronegative than hydrogen, pulls the shared electrons towards itself. As a result, the oxygen atom has a partial negative charge associated with it. The hydrogens (H), on the other hand, are essentially protons and have a partial positive charge associated with them.

2. Hydrogen chloride (HCl)

Hydrogen chloride is a polar covalent compound as the chlorine (Cl) atom is more electronegative than the hydrogen (H) atom. So, chlorine carries a partial negative charge, while hydrogen carries a partial positive charge.

3. Ammonia (NH3)

Ammonia is a polar molecule. The central atom, nitrogen (N), is bonded to three hydrogen (H) atoms. Since N is more electronegative than H, the electrons will tend to hang around the N atom.

4. Hydrogen Bromide (HBr)

The difference in electronegativity between hydrogen (H) and bromine (Br) is not too high. Therefore, the HBr gas has a covalent bond polarized, and the hydrogen atom has a slight positive charge, and bromine has a slight negative charge. As a result, the electron pair is attracted to the bromine.

Polar Covalent Bond Examples

Difference Between Polar and Nonpolar Covalent Bonds [3]

The following table compares and contrasts polar and nonpolar covalent bonds.

Polar Covalent Bond vs. Nonpolar Covalent Bond

PolarNonpolar

Types of atoms

Between two nonmetals with different electronegativities

Between two nonmetals of same electronegativities

Electronegativity difference

0.1 – 2

0

Electron distribution

Asymmetrical. Unequal sharing.

Symmetrical. Equal sharing.

Displacement of shared electrons

Towards the more electronegative atom, making that part negative

No displacement. Electrically neutral.

Dipole moment

Non-zero

Zero

Presence of other types of bonds in compounds

Hydrogen bond

Van der Waals bond

Affinity towards water

Hydrophilic

Hydrophobic

Physical properties of the compounds

High melting and boiling points

Low melting and boiling points

Volatility of liquids

Low volatility

High volatility

Solubility of compounds

Soluble in polar solvents

Soluble in nonpolar solvents

Examples

Water (H2O), ammonia (NH3), and hydrogen chloride (HCl)

Hydrogen (H2), oxygen (O2), and nitrogen (N2)

Polar vs Nonpolar Covalent Bond

References

  1. Chem.libretexts.org
  2. Bbc.co.uk
  3. Stlcc.edu
  4. Saylordotorg.github.io
  5. Chem.ucla.edu
  6. Csus.edu
  7. Chemistry.elmhurst.edu
  8. Chemteam.info
  9. Ch301.cm.utexas.edu
  10. Chemguide.co.uk
  11. Perrylocal.org

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